From 1d73572455fa8f97a24849e5acbab52b8de9bed0 Mon Sep 17 00:00:00 2001
From: Alfredo Garcia <oxarbitrage@gmail.com>
Date: Sat, 26 Jun 2021 20:31:19 -0300
Subject: [PATCH] add enanglement tests

---
 tests/entanglement.rs | 148 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 tests/entanglement.rs

diff --git a/tests/entanglement.rs b/tests/entanglement.rs
new file mode 100644
index 0000000..8bb3706
--- /dev/null
+++ b/tests/entanglement.rs
@@ -0,0 +1,148 @@
+extern crate num;
+extern crate qip;
+
+mod utils;
+
+use qip::{state_ops::from_reals, *};
+
+// Classic and quantum representation of two-qubit initial states.
+struct InitialState {
+    first_bit: u8,
+    first_qubit: Vec<Complex<f64>>,
+    second_bit: u8,
+    second_qubit: Vec<Complex<f64>>,
+}
+
+// Creates the four computational basis states for two-qubit.
+fn initial_states() -> Vec<InitialState> {
+    let basic_state_zero = from_reals(&[1.0, 0.0]);
+    let basic_state_one = from_reals(&[0.0, 1.0]);
+
+    vec![
+        // |00>
+        InitialState {
+            first_bit: 0,
+            first_qubit: basic_state_zero.clone(),
+            second_bit: 0,
+            second_qubit: basic_state_zero.clone(),
+        },
+        // |01>
+        InitialState {
+            first_bit: 0,
+            first_qubit: basic_state_zero.clone(),
+            second_bit: 1,
+            second_qubit: basic_state_one.clone(),
+        },
+        // |10>
+        InitialState {
+            first_bit: 1,
+            first_qubit: basic_state_one.clone(),
+            second_bit: 0,
+            second_qubit: basic_state_zero.clone(),
+        },
+        // |11>
+        InitialState {
+            first_bit: 1,
+            first_qubit: basic_state_one.clone(),
+            second_bit: 1,
+            second_qubit: basic_state_one.clone(),
+        },
+    ]
+}
+
+#[test]
+fn create_entanglement() -> Result<(), CircuitError> {
+    let basis_inputs = initial_states();
+
+    for input in basis_inputs {
+        let mut b = OpBuilder::new();
+        let q1 = b.qubit();
+        let q2 = b.qubit();
+
+        let h1 = q1.handle();
+        let h2 = q2.handle();
+
+        let initial_state = [
+            h1.make_init_from_state(vec![input.first_qubit[0], input.first_qubit[1]])
+                .unwrap(),
+            h2.make_init_from_state(vec![input.second_qubit[0], input.second_qubit[1]])
+                .unwrap(),
+        ];
+
+        // entangle q1 and q2
+        let q1 = b.hadamard(q1);
+        let (q1, q2) = b.cnot(q1, q2);
+
+        // merge
+        let q = b.merge(vec![q1, q2]).unwrap();
+
+        // measure the merged qubit
+        let (q, m) = b.measure(q);
+
+        // run and get measurment
+        let (_, measurements) = run_local_with_init::<f64>(&q, &initial_state).ok().unwrap();
+        let (m, l) = measurements.get_measurement(&m).unwrap();
+
+        // We can't test the measure result as the qubit is in an entangled state but
+        // we know the likelihood of getting one of two possible states is 50-50.
+        assert!(m == 0 || m <= 3);
+        utils::assert_almost_eq(l, 0.5, 10);
+        // TODO: Can we do something better here ?
+    }
+
+    Ok(())
+}
+
+#[test]
+fn measure_entanglement() -> Result<(), CircuitError> {
+    let basis_inputs = initial_states();
+
+    for input in basis_inputs {
+        let mut b = OpBuilder::new();
+        let q1 = b.qubit();
+        let q2 = b.qubit();
+
+        let h1 = q1.handle();
+        let h2 = q2.handle();
+
+        let initial_state = [
+            h1.make_init_from_state(vec![input.first_qubit[0], input.first_qubit[1]])
+                .unwrap(),
+            h2.make_init_from_state(vec![input.second_qubit[0], input.second_qubit[1]])
+                .unwrap(),
+        ];
+
+        // entangle q1 and q2
+        let q1 = b.hadamard(q1);
+        let (q1, q2) = b.cnot(q1, q2);
+
+        // apply the reverse and merge
+        let (q1, q2) = b.cnot(q1, q2);
+        let q1 = b.hadamard(q1);
+        let q = b.merge(vec![q1, q2]).unwrap();
+
+        // measure the merged qubit
+        let (q, m) = b.measure(q);
+
+        // run and get measurment
+        let (_, measurements) = run_local_with_init::<f64>(&q, &initial_state).ok().unwrap();
+        let (m, l) = measurements.get_measurement(&m).unwrap();
+
+        // likelihood is always 1.0
+        utils::assert_almost_eq(l, 1.0, 10);
+
+        // depending on the measurment result we can know with no ambiguity the initial state.
+        let binary_m = format!("{:02b}", m);
+        assert_eq!(
+            binary_m.chars().nth(0).unwrap().to_digit(2).unwrap(),
+            input.second_bit as u32
+        );
+        assert_eq!(
+            binary_m.chars().nth(1).unwrap().to_digit(2).unwrap(),
+            input.first_bit as u32
+        );
+        // TODO: Positions are reversed, check if there is some sort of endianess happening.
+    }
+
+    Ok(())
+}